The aft interstage that originally came with the kit consisted of two molded resin pieces. However, when butted together, there was a half inch gap. I chucked them and used .030" sheet styrene as a replacement. I straightened out the seam later with a knife before applying the individual 1 mm stringers.
One of the other issues with this kit. The white resin piece came with the kit, the drawing shows the true scale, while I made a replacement out of balsa.
An even more out of scale piece. The strip to the left is what the balsa pieces are made out of by laminatinating them three layers wide and three high.